Coordinated Multi-Point transmission with quantized and delayed feedback

Coordinated Multi-Point (CoMP) techniques for LTE-Advanced systems promise high spectral efficiency and enhanced coverage; however, the performance of such systems heavily depends on the feedback quality. In this paper, we study the impact of quantized and delayed feedback on the achievable rate of CoMP systems. We first derive closed-form expressions and tight approximations on the sum-rate of joint transmission processing (JT) and coordinated beamforming (CBF) with imperfect channel state information (CSI). Schemes with increasing interference power at high SNR, i.e. CBF and JT to multiple users, are more sensitive to CSI imperfections than single-user JT. Based on our analytical results, we identify switching points and optimal operating regimes for each scheme and we propose an adaptive mode switching transmit policy. Numerical results show that the number of users to serve under multiuser JT should be optimized based on average SNR, feedback resolution, and delay in order to optimally balance spatial multiplexing gain and diversity.